Process and solution for the aftertreatment of phosphate coatings



July 20, 1965 w. HERBST ETAL 3,

PROCESS AND SOLUTION FOR THE AFTERTREATMENT OF PHOSPHATE COATINGS Original Filed April 13, 1961 PHOSPHATIZED METAL ARTICLES TREATMENT WITH SOLUTIONS OF POLYMERS CONTAINING VINYL PHOSPI'IONIO ACID AND/OR ITS ACID DERIVATIVES AT A TEMPERATURE OF ABOUT 4C. TO ABOUT 70C.

TREATED ARTICLE DRIED AT 'ABOUT 80C.T0 ABOUT lao'c.

INVENTORS Willy Hersf ET-nst Wa rzer M1 @MW United States Patent 3,196,039 PROCESS AND SOLUTION FOR TEE AFTER- TREATMENT OF PHGSPHATE CGATRNGS Wiily Herbst, Hofheim, Taunus, and Ernst Wagner, Frankfurt am Main, Germany, assigrors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany Continuation of application Ser. No. 102,653, Apr. 13, 1961. This application July 7, 1964, Ser. No. 381,614 Claims priority, application Germany, Apr. 16, 1960, F 31,023 5 Ciaims. (Cl. 117-75) The present application is a continuation of our copending application Serial No. 102,653, filed April 13, 1961, now abandoned.

The present invention provides a process for the aftertreatment of phosphatized metal surfaces in order to improve the corrosion protection and an aqueous and/or alcoholic solution for that process, said solution containing at least one polymer or copolymer of vinyl phosphonic acid and, or acid derivatives thereof.

The phosphatizing processes that have been used for decades for the purpose of inhibiting the corrosion of iron and steel surfaces result in phosphate coatings by means of which, on account of their porosity, there is only attained an insutficient protection of the metal in many cases. In order to attain an effective corrosion protection, the phosphatizing process is, therefore, often followed by a rinsing with dilute aqueous chromic acid. The amounts of chromic acid penetrating into the pores of the phosphate coating during this rinsing procedure improve the protective value of these coatings.

This after-treatment, however, involves the inconvenience of a special treatment of the waste water. On account of the considerable toxicity of the compounds of chromium-VI and chromium-III, these compounds must be removed almost quantitatively from the waste Water which entails considerable expense. The chromic acid concentrates used for preparing and replenishing the baths can, moreover, be manipulated with difiiculty only on account of their strongly corrosive properties.

Now we have found a process for the after-treatment of phosphatized metal surfaces in order to improve the corrosion protection in which the disadvantage of the process described above is avoided and which consists in treating the phosphatized metal parts with a solution containing polyvinyl phosphonic acid and/or copolymers of vinyl phosphonic acid and/ or the acid derivatives thereof which contain, per monomer unit, only one free hydroxyl group at the phosphorus atom, advantageously the semi-esters of vinyl phosphonic acid, and the metal parts thus treated are subsequently dried.

The accompanying drawing shows a simplified flow diagram of the invention as described above.

As suitable components for the copolymers of vinyl phosphonic acid and/ or the copolymers of the acid derivatives of vinyl phosphonic acid which contain only one free hydroxyl group per monomer unit at the phosphorus atom, advantageously the semi-esters of vinyl phosphonic acid, there may be used monoor polyunsaturated organic compounds having a substantially polar character, for example acrylic acid, methacrylic acid, and the esters of aliphatic alcohols thereof containing 1 to 5 carbon atoms, the amides and nitriles thereof, also vinyl esters such, for example, as vinyl acetate and vinyl propionate, maleic acid anhydride and crotonic acid.

There may also be used copolymers of vinyl phosphonic acid that are built up from at least three components, for example, from vinyl phosphonic acid, acrylic acid and maleic anhydride or crotonic acid.

It has been found that solutions containing only about 0.000l% by weight of polymer bring about a noticeable improvement in the protection against corrosion as compared with phosphatized metal parts that have not been treated according to the invention.

However, especially those solutions have proved to be useful that contain about 0.008 to about 2% by weight, preferably 0.02 to 0.5% by weight, of polymer.

As solvents for the polyvinyl phosphonic acid and the copolymers cited there may, in addition to water, also be used aliphatic alcohols containing 1 to 4 carbon atoms in the molecule, preferably isopropanol, or mixtures of water and the said aliphatic alcohols.

According to the invention it has also been found to be advantageous to use a solution which contains a wetting agent in addition to the copolymer. As such wetting agents, commercially available products in the usual concentrations may be used when water or a mixture of water and organic solvents in which the predominant part is water are used. Non-ionogenic wetting agents, of example those on the basis of ethylene oxide, have proved to be useful.

The process according to the invention is advantageously carried out such that the phosphatized metal parts are treated with the after-treatment solutions described above for a short time ranging from a few seconds to several minutes, for example, one second to 2 minutes, at a temperature of about 4 C. to about C., preferably about 10 C. to about 25 C., and subsequently dried at about C. to about 180 C., preferably C. to C. The drying depends primarily on the solvent or the solvent mixture used. The phosphatized metal parts can be treated in the usual manner, for example by spraying, immersion or flooding.

The present invention is also directed to the solutions used for carrying out the process, said solutions containing about 0.008 to about 2% by weight of polyvinyl phosphonic acid and/ or copolymers of vinyl phosphonic acid and/or the acid derivatives thereof which contain only one free hydroxyl group at the phosphorus atom, advantageously the semi-esters of vinyl phosphonic acid dissolved in water and/or alcohols containing 1 to 4 carbon atoms and, if desired, commercial wetting agents. Other components of the dissolved copolymer may be organic compounds containing one or more olefinic bonds, especially acrylic acid, methacrylic acid and the esters of aliphatic alcohols thereof containing 1 to 5 carbon atoms, amides and nitriles as well as vinyl esters, maleic acid anhydride and crotonic acid.

The following examples serve to illustrate the invention but they are not intended to limit it thereto:

EXAMPLE 1 Steel plates (of class St VH1 as characterized by Deutsche Industrie Norm (DIN 1623) coated with a Well adhering, light-gray layer of zinc phosphate according to known phosphatizing processes, were, after an intermediate rinsing with cold water, immersed for 20 seconds in a solution containing 0.4 g./l. of a copolymer of vinyl phosphonic acid and acrylic acid (molar ratio 80:20) and dried in the drying closet at 150 C. for 5 minutes. For the purpose of comparison, some of the phosphatized steel plates were immersed, instead of in the aforesaid polymer solution, for 30 seconds in a commercially available after-treatment solution, containing 0.21 g./l. of chromic acid and small quantities of an alkali metal phosphate and having a pH value of 4, and likewise dried in the drying closet at 150 C. for 5 minutes.

The steel plates after-treated according to the two different processes were then coated with an alkyd resin baking varnish in two stages (primer and enamel) at a baking temperature of 145 C., the baking time amounting to 25 minutes in each case, and subjected to the various usual corrosion tests.

It was found that the test samples, both those aftertreated according to the invention and those after-treated subjected to the usual corrosion tests. All steel plates exhibited a very good corrosion protection.

EXAMPLE 3 Steel plates of class St VIII coated with a well adhering 5 l Wl'tll a solution of chromic and, have excellent test values. finely Crystalline dark layer of manganese Phosphate Phosphatized steel plates that have not been after-treated, COTCllng known phOsphatiling Pfmessfis were, after however, only possess an inferior protection against coran intermediate rinsing with cold Wat treated for rosion; their test values are poor. seconds with a solution which was composed as follows:

EXAMPLE 2 10 738 cc. of water 2 Steel plates (of class St VIII) coated according to 3 32 2252 3 3 3 9 h h known phosphatizing processes with a well adhering layer y p 051) an of zinc phosphate having a thickness of about 2 were, The test samples which were then dried in the drying after an intermediate rinsing with cold water, immersed 15 closet at 125 C. for 7 minutes exhibited an excellent for 30 seconds in an aqueous solution containing 0.4 g./l. protection against corrosion. of polyvinyl phosphonic acid and then dried in the drying What is claimed is: closet t 150 C, V 1. A process for improving the corrosion protection of In addition to the aforesaid tests, a further number of phosphatized metal surfaces, which process comprises said steel plates coated with a layer of zinc phosphate after treating said phosphatized metal surfaces at a temwere treated with various other solutions the composiperature of about 4 C. to about 70 C. for a period of tions of which are shown in the following table. In this from one second to two minutes with a solution containtable are indicated in column 2 the concentrations of the ing about 0.008 to about 2 percent by weight of at least respective polymers per liter of solution and the molar one substance selected from the group consisting of (A) ratio for the copolymers, in column 3 the solvent, in a homopolymer of vinyl phosphonic acid and (B) a column 4 the time of immersion, in column 5 the temcopolymer of (1) at least one compound selected from perature of the after-treatment solutions and in column 6 the group consisting of (a) vinyl phosphonic acid and the drying temperatures. (b) the acid derivatives thereof which contain only one Table Time of Bath Drying Test Concentration of polymer per liter/solution Solvent immersion tcmperatemperature C. ture C.

5 grams of polyvinyl phosphonic acid 18 120 15 grams of polyvinyl phosphonic acid 4 180 0.5 gram of a conclymer of vinyl phosphonic 8 150 acid and acrylic acid (molar ratio :40). 4 grams of a copolymer of vinyl phosphcnic do 2 sec 15 140 acid and acrylic acid (molar ratio 80:20). 0.8 gram of a copolymer of vinyl phosphonic do 1 sec 140 agidfmd methacrylic acid (molar ratio 5 :50 f 1 gram of a copolymer of vinyl phosphonic d: 5 sec 30 Z 220 acid and methacrylic acid methyl ester (molar ratio 78:2 g 1.2 grams of a copolymer or vinyl phosphonic do 20 se 16 160 acid and acrylic acid methyl ester (molar ratio 80:20). h 0.6 gram of a copolyrncr of vinyl phosphonic do 2 mm 6 150 acid and vinyl acetate (molar ratio 80:20). i 2.1 grams of a copolymer of vinyl phosphonic Isopropanol- 1 mm 20 acid and acrylic acid (molar ratio 80:20). k 1.1 grams of a copolymer of vinyl phosphonic Ethanolnu- 1 mm 23 89 acid and acrylic acid (molar ratio 80:20). 1 3.0 grams of a copolymcr of vinyl phosphonic 'Mixture of 4 sec 29 140 acid and acrylic acid (molar ratio 80:20). 000 cc. of

water and cc. of butancl. m 0.6 gram of a copolymer of vinyl phosphonic Mixture of 45 sec 20 140 acid and acrylic acid (molar ratio 40:60). 500 cc. of

Water and 500 cc. of isopropanoli n 20.0 grams oiacopolymer of vinyl phosphonic Water 28cc 18 150 acid monoethyl ester and acrylic acid (molar ratio 72:28). 0 1 009 gram of a copolymer of vinyl phosphonic Mixture of 30 Seen 18 acid monooctyl ester and vinyl acetate 258 cc.of (molar ratio 81:10) water and 742 cc. of isopropanol. p 0.4 gram of a copolymer of vinyl phosphonic Mixture of 10 sec 18 acid and acrylic acid amide (molar ratio 369 cc. of 83:17) water and 631 cc. of isopropanol.

1 These solutions contain also a non-ionogenic wetting agent on the basis of ethylene oxide in a concentration of 1% (b) or 60% (0), calculated on the polymer concentration.

2 Drying time 3 minutes. 3 Hot-air blower.

After drying, all steel plates treated with the solution-s enumerated in the table as given above were coated with an alkyd resin baking varnish in two stages (primer and enamel) at a baking temperature of C., the baking time amounting to 25 minutes in each case,

free hydroxyl group per monomer unit at the phosphorus atom, and, as comonomer, (2) at least one compound selected from the group consisting of (a) acrylic acid, (b) methacrylic acid, (c) esters of acrylic acid and methaand 75 crylic acid with aliphatic alcohols containing one to five carbon atoms, (d) amides of acrylic acid and methacrylic acid, (e) vinyl acetate, (f) maleic acid anhydride, and (g) crotonic acid, and then drying the treated surfaces at a temperature between about 80 C. and about 180 C.

2. A process as in claim 1 wherein said solution contains, as a solvent, at least one member selected from the group consisting of water and aliphatic alcohols containing one to four carbon atoms.

3. A process as in claim 1 wherein said solution additionally contains a Wetting agent.

4. An after-treating solution for improving the corrosion protection of phosphatized metal surfaces, which solution contains, as a solvent, at least one member selected from the group consisting of water and aliphatic alcohols containing one to four carbon atoms, and, as a solute, about 0.008 to about 2 percent by weight of at least one substance selected from the group consisting of 6 (A) a homopolyrner of vinyl phosphonic acid and (B) a copolymer of (1) at least one compound selected from the group consisting of (a) vinyl phosphonic acid and (b) the acid derivatives thereof which contain only one free hydroxyl group per monomer unit at the phosphorus atom, and, as cornonomer, (2) at least one compound selected from the group consisting of (a) acrylic acid, (b) methacrylic acid, (c) esters of acrylic acid and methacrylic acid with aliphatic alcohols containing one to five carbon atoms, ((1) amides of acrylic acid and methacrylic cid, (e) vinyl acetate, (f) maleic acid anhydride, and (g) crotonic acid.

5. A solution as in claim 4 which additionally contains a wetting agent.

No references cited.

RICHARD D. NEVIUS, Primary Examiner. 

1. A PROCESS FOR IMPROVING THE CORROSION PROTECTION OF PHOSPHATIZED METAL SURFACES, WHICH PROCESS COMPRISES AFTER-TREATING SAID PHOSPHATIZED METAL SURFACES AT A TEMPERATURE OF ABOUT 4*C. TO ABOUT 70*C. FOR A PERIOD OF FROM ONE SECOND TO TWO MINUTES WITH A SOLUTION CONTAINING ABOUT 0.008 TO ABOUT 2 PERCENT BY WEIGHT OF AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF (A) A HOMOPOLYMER OF VINYL PHOSPHONIC ACID AND (B) A COPOLYMER OF (1) AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF (A) VINYL PHOSPHONIC ACID AND (B) THE ACID DERIVATIVES THEREOF WHICH CONTAIN ONLY ONE FREE HYDROXYL GROUP PER MONOMER UNIT AT THE PHOSPHORUS ATOM, AND, AS COMONOMER, (2) AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF (A) ACRYLIC ACID, (B) METHACRYLIC ACID, (C) ESTERS OF ACRYLIC ACID AND METHACRYLIC ACID WITH ALIPHATIC ALCOHOLS CONTAINING ONE TO FIVE CARBON ATOMS, (D) AMIDES OF ACRYLIC ACID AND METHACRYLIC ACID, (E) VINYL ACETATE, (F) MALEIC ACID ANHYDRIDE, AND (G) CROTONIC ACID, AND THEN DRYING THE TREATED SURFACES AT A TEMPERATURE BETWEEN ABOUT 80*C. AND ABOUT 180*C. 